For supply of power to a load such as a motor, an inverter circuit using a semiconductor switching element such as a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT) has been used. An intelligent power module (IPM) with an inverter circuit is a power module in which a driving circuit and a protection circuit are housed in one package together with the inverter circuit of a general type. The driving circuit is typically configured with a low voltage integrated circuit (LVIC) and a high voltage integrated circuit (HVIC). Typical protective operation (specifically, the operation of the protection circuit) is to prohibit generation of a signal for placing the semiconductor switching element in an ON state on the occurrence of an overcurrent resulting from fluctuations of load-side operation.
According to Japanese Patent Application Laid-Open No. 2017-5125, for example, a first semiconductor chip and a second semiconductor chip are arranged in a package. The first semiconductor chip includes a power transistor that drives an external load, a driving circuit that drives the power transistor, a current sense circuit that monitors a current flowing in the power transistor, and a protection circuit that prevents breakdown of the power transistor.
The technique described in the foregoing publication is intended to prevent breakdown of an IPM (power semiconductor device) with the power transistor (semiconductor switching element). However, this technique does not give consideration to prevention of breakdown of a load to be caused by an overcurrent. If the occurrence of an overcurrent is limited to an extremely short duration (typically, some microseconds), breakdown of the load (typically, a motor) is unlikely to occur, so that preventing breakdown of the power semiconductor device is sufficient in many cases. By contrast, if the occurrence of an overcurrent lasts for a longer duration (typically, some milliseconds), further consideration should be given to breakdown of the load. Such consideration is required to be given, particularly if a current value that can be sustained by the load is lower than a current value that can be sustained by the power semiconductor device. The reason for this is that, if a current value at the load exceeds a permissible value but this current value is smaller than a value assumed to be a permissible value for the power semiconductor device, protective operation is not started. Hence, the foregoing conventional technique has the risk of breakdown of the load.